1. Field of Invention
The present disclosure relates in general to a system for fracturing a subterranean formation by creating perforations in a wellbore that intersects the formation, where the perforations extend along the circumference of the wellbore and at substantially the same depth.
2. Description of Prior Art
Perforating systems are typically used for forming hydraulic communication passages, called perforations, in wellbores drilled through earth formations so that predetermined zones of the earth formations can be hydraulically connected to the wellbore. Perforations are needed because wellbores are typically lined with a string of casing that is cemented to the wellbore wall. Reasons for cementing the casing against the wellbore wall includes retaining the casing in the wellbore and hydraulically isolating various earth formations penetrated by the wellbore. Without the perforations oil/gas from the formation surrounding the wellbore cannot make its way to production tubing inserted into the wellbore within the casing.
Perforating systems typically include one or more perforating guns connected together in series to form a perforating gun string, which can sometimes surpass a thousand feet of perforating length. The gun strings are usually lowered into a wellbore on a wireline or tubing, where the individual perforating guns are generally coupled together by connector subs. Included with the perforating gun are shaped charges that typically include a housing, a liner, and a quantity of high explosive inserted between the liner and the housing. When the high explosive is detonated, the force of the detonation collapses the liner and ejects it from one end of the charge at very high velocity in a pattern called a jet that perforates the casing and the cement and creates a perforation that extends into the surrounding formation. Each shaped charge is typically attached to a detonation cord that runs axially within each of the guns.
The perforations are sometimes elongated into subterranean fractures by adding a pressurized fracturing fluid to the wellbore. Elongating the perforations increases the surface area of the formation that is in communication with the wellbore, therefore increasing fluid flow from the formation, which in turn increases hydrocarbon production. Sometimes a particulate, referred to as a proppant, is introduced into the perforations and fractures for structural support and to maintain an open passageway for connate fluid into the wellbore.